The extrusion of alginate solutions into an aqueous solution containing calcium ions to form yarns of calcium alginate filaments is known, for example, from British Pat. Nos. 567,641, 568,177, 571,657 and 624,987. The alginate yarn when formed into a fabric is useful as a haemostatic wound dressing as described in British Pat. No. 621,320. Such fabrics have generally been prepared by knitting a yarn of calcium alginate filaments and partially converting the calcium alginate to the sodium form to form a calcium sodium alginate containing, for example, 30-70 percent by weight of the carboxy groups of the alginate in the calcium form. This process is difficult in practice. The alginate fibres in the calcium form are brittle and in the sodium calcium alginate form they are very weak and sensitive to moisture.